1. Field of the Invention
The disclosures herein relate to an in-vehicle device, a recording medium, and a keyless entry system.
2. Description of the Related Art
Conventionally, keyless entry systems that include in-vehicle devices installed in vehicles and portable devices carried by users have been utilized. In the keyless entry systems, in order to control turning on or off of lamps and locking and unlocking of a vehicle, it is important to identify the location of a portable device (a user) with respect to the vehicle. Conventionally, a method for identifying the location of a portable device with respect to a vehicle has been proposed. In the conventional method, an in-vehicle device transmits request signals from a plurality of respective transmitting antennas, the portable device measures received signal strength indicator (RSSI) of each of the request signals, and transmits an answer signal that includes the received signal strengths, and the in-vehicle device identifies the location of the portable device based on the received signal strengths included in the answer signal.
However, in the above conventional method, if the portable device fails to receive a request signal due to a malfunction or a communication failure of a transmitting antenna, a received signal strength of the request signal is not included in an answer signal, thus causing the in-vehicle device to be unable to identify the location of the portable device. In other words, even if other request signals can be received, the in-vehicle device is unable to identify the location of the portable device.